In a general manner, the process of manufacturing thermosetting resin articles by pultrusion is known. The usual process consists of impregnating a plurality of fibers with resin, and then passing the bulk substance into a heated chamber. At the chamber exit, the fibers coated with resin enter a heated device which gives the final shape to the product being produced, which is cured as it emerges from the device. This is done in a continuous process.
Generally, a "prepreg" is used in a pressure molding process. A prepreg is a resin-coated cloth or fiber. The resin is usually applied from a solvent solution, then dried or partially cured. In the partially cured stage it is easy to handle and will soften and mold upon heating. In the automotive industry, for example, prepregs are generally known as sheet molding compounds which are large enough sheets to mold into doors, hoods, fenders and body parts in general. Prepregs are also valuable in aircraft and aerospace industries.
The usual method of pultrusion involves the pulling of a prepreg or resin coated fibers through a mold to form a shaped article in a continuous process. This method is used to form many types of articles known in the art, and often involves pulling a prepreg through a rigid metal forming device. This way a certain shape is attained (e.g., pulling a prepreg through a mold shaped like an "I" to form an "I-beam" for construction). For a discussion regarding this technology see U.S. Pat. No. 3,567,814 to Glesner; U.S. Pat. No. 4,209,482 to Schwarz; and U.S. Pat. No. 5,084,222 to Glemet et al., all incorporated herein by reference. Additionally, for a detailed discussion of thermosets and thermosetting technology, see "Advanced Thermoset Composites: Industrial and Commercial Applications", edited by Margolis, James M., Van Nostrand Reinhold Company (New York) 1986, incorporated herein by reference.
All prior art methods, however, are limited in that all resin saturated fibers are pulled through a single rigid mold or die, and are cured to the specific shape of the mold or die in a continuous process. Prepreg is also made by pultrusion by shaping with a rigid die or mold and "staged" for later use. The term "staged" refers to the partially cured condition, which permits the prepreg to be manipulated to a desired shape. Staging can be accomplished by temperature control, or using a chemical catalyst, as known in the art. Once the prepreg is formed into a desired shape, it is then fully cured and retains its shape. Prepreg made by this method results in resin tackiness and must be separated with release sheets and frozen for shipment to users.
The present invention permits a much broader range of molding by providing a method of pultrusion into a flexible mold. Therefore, after the resin coated fibers are pulled into the flexible mold, they can be shaped or maneuvered into any desired form and staged with a latent catalyst for subsequent use, thus avoiding contamination of resin onto one's hands or clothes. The flexible mold is then removed by chemical or mechanical means.
Accordingly, it is an object of the present invention to provide a method of pultrusion comprised of pulling resin coated fibers into a flexible mold.
A further object of the present invention is to provide a method of pultrusion capable of providing a curable resin composition in a flexible and maneuverable mold, said mold capable of being manipulated manually without the need for hand or equipment protection.
An additional object of the present invention is to provide a method of pultrusion comprised of pulling resin impregnated fibers into a flexible mold, shaping said mold into a desired shape, and removing said flexible mold by mechanical or chemical means.